The field of minimally invasive surgery, including without limitation laparoscopic and endoscopic surgery, has recently experienced dramatic growth. Procedures such as laparoscopic appendectomy and cholecystectomy (removal of the gall bladder), and various gynecological procedures have become widely adopted in clinical practice. When performed safely, the minimally invasive alternatives to traditional surgical intervention can reduce costs of care by shortening hospital stays and recuperation times. They also provide collateral benefits such as reduced patient discomfort and better cosmetic results, i.e., reduced scarring. There is strong demand being generated by patients for these alternate procedures.
Minimally invasive procedures frequently begin with obtaining access to a body cavity, for example, the abdomen, through the use of specialized trocars and surgical needles. Typically, for one example, a laparoscopic procedure begins with the insertion of a specialized insufflation needle, commonly known as a Verres needle, into the abdominal cavity. Once inserted, carbon dioxide is introduced through the needle (insufflation) to create what is called a pneumoperitoneum. This distends the abdominal wall to separate it from the underlying vital organs. The pneumoperitoneum is designed to protect the abdominal contents during insertion of the trocar.
The next step is to establish one or more portals through which various diagnostic and/or operating instruments can be inserted and, once inside the body, manipulated to perform the desired function. Devices for creating such portals are commonly known as trocars, which include a puncturing tool having a sharp tip that is pressed into and through the tissue, and a hollow sleeve or cannula. The puncturing tool and sleeve are forced into the skin and through the tissue in combination. Once the tool has punctured the tissue and passed into the body cavity, it is removed, leaving the sleeve as a rigid conduit forming the portal. The puncturing tool tip is commonly known as a trocar tip, which is secured to the end of a structure called a sheath or an obturator or obturator tube.
Typically, a rigid laparoscope is the first instrument inserted into the body cavity through the established portal. The laparoscope provides for direct visualization of the body cavity. A miniature video camera is commonly attached to the laparoscope eyepiece so all subsequent procedures can be easily viewed on a video screen (CRT). Other portals may be created in a similar fashion for the insertion of additional instruments having diagnostic and/or surgical functions.
In addition to laparoscopic surgery, there are other indications for penetrating a body cavity with a trocar or other puncturing tool such as a surgical needle. Examples include paracentesis and thoracentesis whereby a needle is inserted into the abdominal or thoracic cavity for the purpose of withdrawing collections of fluid which may be abnormal.
One problem with insertion of the Verres needle, trocar, and similar puncturing tools is that the initial puncture (insertion) is performed blind. Thus, it can be difficult to tell with certainty that the needle or trocar tip has entered the desired body cavity. This can lead to a variety of complications such as inadvertent insufflation of extraperitoneal tissues with CO.sub.2. If this occurs, the patient may experience subcutaneous emphysema (gas in the tissues under the skin) or even lethal hypercarbia (high levels of CO.sub.2 in the blood).
Other complications include punctured abdominal viscus (e.g., bowel) or vascular injury (e.g., aorta). Although relatively rare, these complications carry significant morbidity and mortality. This is especially problematic as laparoscopic and other minimally invasive surgical procedures are increasingly performed out of the hospital environment where sophisticated emergency backup may not be readily available. Although ultrasound or fluoroscope techniques may be of some assistance, they are difficult to use, add complexity to the procedure and require additional, expensive equipment and personnel trained to operate the equipment.
Devices to enhance the safety of trocar insertion are known. For example, U.S. Pat. Nos. 5,114,407, 5,104,382, 5,116,353, 4,601,710 and 5,066,288 refer to safety trocars having either spring-loaded shields or self-retracting trocar tips either to cover or remove the sharp tip of the trocar after it penetrates a body cavity and prevent inadvertent tissue injury. The safety mechanisms are typically cocked prior to use and designed to engage after a loss of tissue resistance occurs, such as that which usually occurs when a body cavity is entered. Loss of tissue resistance may be sensed, for example, by loading on a spring release mechanism.
These devices suffer from several drawbacks. First, the safety mechanisms can operate to obstruct the trocar tip before it actually (or fully) penetrates the tissue into the body cavity. Conversely, the mechanisms may fail to engage after the body cavity is entered such that relying upon the engagement of such devices as an indicator of penetration may result in erroneously continuing to advance the sharp trocar.
U.S. Pat. No. 4,191,191 refers to a laparoscopic trocar with a screw mechanism to effect gradual penetration into the abdominal cavity. One disadvantage of this device is that no mechanism is provided for ensuring that the trocar has actually entered the abdominal cavity.